1. Field of the Invention
The treatment of many cellular disorders, for example, tumors, and hyperproliferative disease, e.g. psoriasis, involves the use of cytotoxic drugs. These drugs exert their activity in a variety of ways, usually interfering with a cellular function essential for the replication and/or viability of the cell. In many, if not most instances, the drug is not specific for the abnormal cell, but rather tends to exert its effectiveness due to the more rapid proliferation of the abnormal cell, as compared to normal cells. While many organs of the body of a mammalian host regenerate cells rather slowly, there are also other organs, particularly bone marrow, which involve rapid proliferation of stem cells. Therefore, the cytotoxic agents not only can detrimentally affect the slowly regenerating cells, but also have a particularly pernicious effect on the immune system.
Despite the many disadvantages and side effects of employing the strongly cytotoxic drugs, they have found extensive application because they have provided positive results. However, there is substantial interest in being able to employ the drugs in a manner which directs their activity toward the abnormal cells, while simultaneously protecting sensitive normal cells, both in the vicinity of and distant from the site of application.